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<ul id="index">
  <li><a href="#NAME">NAME</a></li>
  <li><a href="#DESCRIPTION">DESCRIPTION</a>
    <ul>
      <li><a href="#Identity">Identity</a></li>
      <li><a href="#Supported-parameters">Supported parameters</a></li>
    </ul>
  </li>
  <li><a href="#NOTES">NOTES</a></li>
  <li><a href="#EXAMPLES">EXAMPLES</a></li>
  <li><a href="#CONFORMING-TO">CONFORMING TO</a></li>
  <li><a href="#SEE-ALSO">SEE ALSO</a></li>
  <li><a href="#HISTORY">HISTORY</a></li>
  <li><a href="#COPYRIGHT">COPYRIGHT</a></li>
</ul>

<h1 id="NAME">NAME</h1>

<p>EVP_KDF-KB - The Key-Based EVP_KDF implementation</p>

<h1 id="DESCRIPTION">DESCRIPTION</h1>

<p>The EVP_KDF-KB algorithm implements the Key-Based key derivation function (KBKDF). KBKDF derives a key from repeated application of a keyed MAC to an input secret (and other optional values).</p>

<h2 id="Identity">Identity</h2>

<p>&quot;KBKDF&quot; is the name for this implementation; it can be used with the EVP_KDF_fetch() function.</p>

<h2 id="Supported-parameters">Supported parameters</h2>

<p>The supported parameters are:</p>

<dl>

<dt id="mode-OSSL_KDF_PARAM_MODE-UTF8-string">&quot;mode&quot; (<b>OSSL_KDF_PARAM_MODE</b>) &lt;UTF8 string&gt;</dt>
<dd>

<p>The mode parameter determines which flavor of KBKDF to use - currently the choices are &quot;counter&quot; and &quot;feedback&quot;. &quot;counter&quot; is the default, and will be used if unspecified.</p>

</dd>
<dt id="mac-OSSL_KDF_PARAM_MAC-UTF8-string">&quot;mac&quot; (<b>OSSL_KDF_PARAM_MAC</b>) &lt;UTF8 string&gt;</dt>
<dd>

<p>The value is either CMAC or HMAC.</p>

</dd>
<dt id="digest-OSSL_KDF_PARAM_DIGEST-UTF8-string">&quot;digest&quot; (<b>OSSL_KDF_PARAM_DIGEST</b>) &lt;UTF8 string&gt;</dt>
<dd>

</dd>
<dt id="cipher-OSSL_KDF_PARAM_CIPHER-UTF8-string">&quot;cipher&quot; (<b>OSSL_KDF_PARAM_CIPHER</b>) &lt;UTF8 string&gt;</dt>
<dd>

</dd>
<dt id="properties-OSSL_KDF_PARAM_PROPERTIES-UTF8-string">&quot;properties&quot; (<b>OSSL_KDF_PARAM_PROPERTIES</b>) &lt;UTF8 string&gt;</dt>
<dd>

</dd>
<dt id="key-OSSL_KDF_PARAM_KEY-octet-string">&quot;key&quot; (<b>OSSL_KDF_PARAM_KEY</b>) &lt;octet string&gt;</dt>
<dd>

</dd>
<dt id="salt-OSSL_KDF_PARAM_SALT-octet-string">&quot;salt&quot; (<b>OSSL_KDF_PARAM_SALT</b>) &lt;octet string&gt;</dt>
<dd>

</dd>
<dt id="info-OSSL_KDF_PARAM_INFO-octet-string">&quot;info (<b>OSSL_KDF_PARAM_INFO</b>) &lt;octet string&gt;</dt>
<dd>

</dd>
<dt id="seed-OSSL_KDF_PARAM_SEED-octet-string">&quot;seed&quot; (<b>OSSL_KDF_PARAM_SEED</b>) &lt;octet string&gt;</dt>
<dd>

<p>The seed parameter is unused in counter mode.</p>

</dd>
<dt id="use-l-OSSL_KDF_PARAM_KBKDF_USE_L-integer">&quot;use-l&quot; (<b>OSSL_KDF_PARAM_KBKDF_USE_L</b>) &lt;integer&gt;</dt>
<dd>

<p>Set to <b>0</b> to disable use of the optional Fixed Input data &#39;L&#39; (see SP800-108). The default value of <b>1</b> will be used if unspecified.</p>

</dd>
<dt id="use-separator-OSSL_KDF_PARAM_KBKDF_USE_SEPARATOR-integer">&quot;use-separator&quot; (<b>OSSL_KDF_PARAM_KBKDF_USE_SEPARATOR</b>) &lt;integer&gt;</dt>
<dd>

<p>Set to <b>0</b> to disable use of the optional Fixed Input data &#39;zero separator&#39; (see SP800-108) that is placed between the Label and Context. The default value of <b>1</b> will be used if unspecified.</p>

</dd>
</dl>

<p>Depending on whether mac is CMAC or HMAC, either digest or cipher is required (respectively) and the other is unused.</p>

<p>The parameters key, salt, info, and seed correspond to KI, Label, Context, and IV (respectively) in SP800-108. As in that document, salt, info, and seed are optional and may be omitted.</p>

<p>&quot;mac&quot;, &quot;digest&quot;, cipher&quot; and &quot;properties&quot; are described in <a href="../man3/EVP_KDF.html">&quot;PARAMETERS&quot; in EVP_KDF(3)</a>.</p>

<h1 id="NOTES">NOTES</h1>

<p>A context for KBKDF can be obtained by calling:</p>

<pre><code> EVP_KDF *kdf = EVP_KDF_fetch(NULL, &quot;KBKDF&quot;, NULL);
 EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);</code></pre>

<p>The output length of an KBKDF is specified via the <code>keylen</code> parameter to the <a href="../man3/EVP_KDF_derive.html">EVP_KDF_derive(3)</a> function.</p>

<p>Note that currently OpenSSL only implements counter and feedback modes. Other variants may be supported in the future.</p>

<h1 id="EXAMPLES">EXAMPLES</h1>

<p>This example derives 10 bytes using COUNTER-HMAC-SHA256, with KI &quot;secret&quot;, Label &quot;label&quot;, and Context &quot;context&quot;.</p>

<pre><code> EVP_KDF *kdf;
 EVP_KDF_CTX *kctx;
 unsigned char out[10];
 OSSL_PARAM params[6], *p = params;

 kdf = EVP_KDF_fetch(NULL, &quot;KBKDF&quot;, NULL);
 kctx = EVP_KDF_CTX_new(kdf);
 EVP_KDF_free(kdf);

 *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
                                         &quot;SHA2-256&quot;, 0);
 *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC,
                                         &quot;HMAC&quot;, 0);
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
                                          &quot;secret&quot;, strlen(&quot;secret&quot;));
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
                                          &quot;label&quot;, strlen(&quot;label&quot;));
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
                                          &quot;context&quot;, strlen(&quot;context&quot;));
 *p = OSSL_PARAM_construct_end();
 if (EVP_KDF_derive(kctx, out, sizeof(out), params) &lt;= 0)
     error(&quot;EVP_KDF_derive&quot;);

 EVP_KDF_CTX_free(kctx);</code></pre>

<p>This example derives 10 bytes using FEEDBACK-CMAC-AES256, with KI &quot;secret&quot;, Label &quot;label&quot;, and IV &quot;sixteen bytes iv&quot;.</p>

<pre><code> EVP_KDF *kdf;
 EVP_KDF_CTX *kctx;
 unsigned char out[10];
 OSSL_PARAM params[8], *p = params;
 unsigned char *iv = &quot;sixteen bytes iv&quot;;

 kdf = EVP_KDF_fetch(NULL, &quot;KBKDF&quot;, NULL);
 kctx = EVP_KDF_CTX_new(kdf);
 EVP_KDF_free(kdf);

 *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_CIPHER, &quot;AES256&quot;, 0);
 *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC, &quot;CMAC&quot;, 0);
 *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MODE, &quot;FEEDBACK&quot;, 0);
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
                                          &quot;secret&quot;, strlen(&quot;secret&quot;));
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
                                          &quot;label&quot;, strlen(&quot;label&quot;));
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
                                          &quot;context&quot;, strlen(&quot;context&quot;));
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SEED,
                                          iv, strlen(iv));
 *p = OSSL_PARAM_construct_end();
 if (EVP_KDF_derive(kctx, out, sizeof(out), params) &lt;= 0)
     error(&quot;EVP_KDF_derive&quot;);

 EVP_KDF_CTX_free(kctx);</code></pre>

<h1 id="CONFORMING-TO">CONFORMING TO</h1>

<p>NIST SP800-108, IETF RFC 6803, IETF RFC 8009.</p>

<h1 id="SEE-ALSO">SEE ALSO</h1>

<p><a href="../man3/EVP_KDF.html">EVP_KDF(3)</a>, <a href="../man3/EVP_KDF_CTX_free.html">EVP_KDF_CTX_free(3)</a>, <a href="../man3/EVP_KDF_CTX_get_kdf_size.html">EVP_KDF_CTX_get_kdf_size(3)</a>, <a href="../man3/EVP_KDF_derive.html">EVP_KDF_derive(3)</a>, <a href="../man3/EVP_KDF.html">&quot;PARAMETERS&quot; in EVP_KDF(3)</a></p>

<h1 id="HISTORY">HISTORY</h1>

<p>This functionality was added to OpenSSL 3.0.</p>

<h1 id="COPYRIGHT">COPYRIGHT</h1>

<p>Copyright 2019-2021 The OpenSSL Project Authors. All Rights Reserved. Copyright 2019 Red Hat, Inc.</p>

<p>Licensed under the Apache License 2.0 (the &quot;License&quot;). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <a href="https://www.openssl.org/source/license.html">https://www.openssl.org/source/license.html</a>.</p>


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